if strcmp(signal, 'off')
 I = std_IQ*randn(M, N) ;
 Q = std_IQ*randn(M, N) ;
 X2 = I.^2 + Q.^2;
 X2max(j) = max(max(X2)); 
elseif strcmp(signal, 'on')
 dtau = tau(j) - tau_tilda_m;
 domega = omega(j) - omega_tilda_m;
 I = A*L/2 * ro(dtau) .* sinc(domega*T/2 /pi) .* cos(domega*T/2 ...
+ dphi(j)) + std_IQ*randn(M, N) ;
 Q =- A*L/2 * ro(dtau) .* sinc(domega*T/2 /pi) .* sin(domega*T/2 ...
 + dphi(j)) + std_IQ*randn(M, N) ;
 X2 = I.^2 + Q.^2;
 X2max(j) = max(max(X2));
end 
